Where will the weight come from for the 4Kg beater? You cant lose 500g by changing from a S900 to a HK-40... can you?
I am about to throw up the next iteration of Conker 3. I seem to be stuck with a 3kg beater simply cos of the 4WD but I may be able to mess with it to push that up! It will also be able to push like crazy if need be cos of the two 18v 775 motors on 16:1!